HYDROLOGICAL MODELING OF THE HIGH FLOW IN MARITZA RIVER BASIN IN AUGUST 2005 ANALYSIS OF THE INFLUENCE OF THE TOPOLNITZA RESERVOIR Eram Artinian National Institute of Meteorology and Hydrology of Bulgaria – regional centre Plovdiv [email protected] Abstract High waters that streamed down the beds of nearly all rivers of Maritza river basin and especially down the bed of Topolnitza river from the fourth till the seventh day of August 2005 were an event of major influence upon all aspects of life in this region of Bulgaria. They were caused by the extreme amount of rainfall in the areas of Ihtiman, Kostenets, Dolna Banya etc., in the North-West part of the river basin on the fourth and the fifth day of August and in the Rhodopy and the Gornotrakiyska valley regions on the following days. The high water stream itself caused overflow of the rivers Mativir, Topolnitza and Maritza in a number of areas downstream of their river beds and caused substantial material damages and even took away a human life. In the Rhodopi region, the waters of Chepinska, Cherna, Shirokolashka and Chepelarska rivers also caused substantial disruption of their river banks. Supporting walls and other items of infrastructure were pulled down at many places. Large areas of road covering sank down. Considerable material damages were caused in the towns of Smolyan, Velingrad and Chepelare. To find the numerical expression of the approximate flow in the river network near the city of Plovdiv for the purposes of this research, the physical processes in the ground layer of the atmosphere, in the ground – under ground combination and in the river network for the period from the first till the tenth of August were simulated. Streamflow is calculated for profiles with monitored river flow and in separate, additional profiles like outlets of rivers to Maritza (Ochushnitza, Yadenitza, Luda Yana, Vacha). The purpose of this analysis is to explain the genesis of the high wave rather than to give a precise numerical expression of its existence. Therefore, the numerical results achieved during the modeling shall be considered as tentative. Due to the decisive influence of the artificial lake of Topolnitza over the hydrological processes in the river beds of the rivers Topolnitza and Maritza, an evaluation was made in this research of the influence of the Topolnitza reservoir over the maximum water quantities that flew down through the cities of Pazardzhik and Plovdiv. The natural water feed at the wall of the artificial lake of Topolnitza was simulated. The daily average flow of the Maritza river at the city of Pazardzhik and at the city of Plovdiv was simulated on the following three conditional hypothesis: A) natural flow down the whole basin with the exclusion of the Vacha cascade; B) Evaluation of the regulative influence of the artificial lake of Topolnitza by data given by “Irrigation systems” PLC; C) option with closed valves of the artificial lake. Numerical models adapted for the basin of Maritza were used for the simulation. These models have been developed by CNRM Météo-France and “Ecole de Mines de Paris” (France). The first organization is a research center at the National Institute of Meteorology of France and there the ISBA (Interface Soil Biosphere Atmosphere) scheme has been developed. The second one is the Higher Institute of Mining – Paris, where the hydrological and hydro geological method Modcou has been developed. The scheme and the model are consecutively connected and are usually used jointly for hydrological modeling and prognosis on national scale in France, Canada and other countries. Representation of the ISBA scheme: The ISBA scheme simulates the single dimensional model of the interface between atmosphere and soil. It includes the influence of the periodical vegetation at the calculation of the actual evaporation, which in general, consists of evaporation from the soil surface, from the foliar mass and transpiration of vegetation. The soil characteristics are given as parameters through the mechanical composition of the types of soil. The scheme calculates the water contents and height (thickness) of the snow pack and respectively the snow piling and the snow melting during the autumn – spring period. The problem solved by the scheme ISBA (figure 1) is to determine the water quantity for surface flow (Qr) and the infiltration (D) by given values of: quantity of rainfall, temperature of air, moisture of air, and other meteorological parameters, variable in space and time. Figure 1: scheme of joint application ISBA – Drainage reservoirs – Modcou During the modeling of the processes at the surface of the Maritza river basin, the single dimensional scheme ISBA (Noilhan and Mahfouf, 1995) is applied on 638 cells with dimensions of 8x8 kilometers. The scheme uses input data with different intervals in time and calculations are performed at intervals of 5 minutes. Representation of the hydrological model Modcou Modcou is a hydrodynamic hydrological and hydro geological model with distributed parameters (Ledoux, 1980). The problem solved by the model is to transport the calculated water volumes through the mathematically represented river network and in the end to calculate the average daily flow amount at certain points of the river network without prejudice to whether monitoring was carried out there or not. The hydrological network is represented by a tree-like network of cells (figure 2). Each one of them receives the surface and the soil water flow and transfers it to the next cell down the river. The flow velocity is determined by isochronal zones (Ledoux, et al. 1989) – with equal times of runoff to the river mouth. On the grounds of a numerical model of the terrain for each call, the time for runoff to the outlet of the cachement area is calculated as part of the maximum runoff time. Figure 2: The network of cells of the hydrological model and hydrographic network of the Maritza river basin to the city of Edirne. The part of the basin near the city of Plovdiv is given in blue. Simulation is made at the points with red color where streamflow measurements are also available. The maximum runoff time is calibrated in an experimental way. The network of surface cells for the Maritza river basin comprises of total 11661 cells with dimensions from 1x1 kilometer to 4x4 kilometers and 2387 of those are river cells. The time interval of the model by which the outflow is calculated is one day an in this research, the average twenty four hour outflow (m3/sec) is calculated for 77 of the river cells. Hydrological modeling of the river flow for the Maritza river basin down to the city of Plovdiv. Preparation of the input data In this particular case the values of temperature, air humidity, wind velocity and radiation, necessary for the input of the system are received as output data from a short-term meteorological model ALADIN, used by the National Institute of Meteorology and Hydrology (NIMH) for meteorological prognosis. In previous research works it was pointed out that the output fields from ALADIN for temperature and humidity of the near the ground air at time intervals of three hours, as well as those for the sun and air radiation and wind velocity may be used for hydrological modeling (Noilhan, 2002; Artinyan, et al. 2003). The necessary space fields of rainfall are received by space interpolation of the combined rainfall measuring measurements, carried out for the period from the first to the seventh of August by the monitoring networks of NIMH and “Irrigation systems” PLC. These round the clock sums of rainfall quantities (from 07:30 a.m. till 07:30 a.m. of the next day) were critically analyzed. For the purpose of not omitting of measurements and to achieve a satisfactory density of the actually measured values of rainfall quantities, in some cases the data were logically corrected. For the achievement of a space field, rainfall measurements were interpolated by the technology of “point” krigging. This technology gives advantage to experimental values, whilst the “block” krigging gives advantage to the general characteristics of the field and smooths the iso-lines. It must be pointed out that it is technologically impossible and not necessary for the interpolated field to reflect with absolute precision each one of the measured values. Practical experience shows that the field of rainfall has an ultimately uneven distribution in space. Different measurement points in one and the same area show substantially different valued of the measured rainfall quantities for one and the same time. In such cases, prior to the interpolation of the respective points, they are assigned their average values. Such are the cases with Ihtiman and Etropole, where the data given by NIHM and “Irrigation systems” PLC are substantially different for some of the days between the fourth and the seventh of August. Calibration of the system with drainage reservoirs and maximum runoff time At the calibration of the system with drainage reservoirs (SDR) for long periods of time – two and more years, parameters are determined which reflect the average status of soil humidity, rainfall with average intensity and low to average high waters. In this particular case, the intense (extreme) rainfall in the Topolnitza basin and the upper stream of Maritza (above the town of Belovo), the SDR parameters for the above named areas had to be calibrated once again. The daily average streamflow quantities calculated by NIMH, which strictly reflect the direct measurements of the flow, were used as base. It was determined that the maximum runoff time to the city of Edirne, which is an important parameter for the high wave that went downstream is a little over five days, but not as the prior to that determined six days for low and average waters.